Works mostly

server/topic.go

@@ -0,0 +1,68 @@
+package server
+
+import (
+	"context"
+	"errors"
+	"log"
+	"math/rand"
+	"sync"
+	"time"
+)
+
+type topic struct {
+	id          string
+	subscribers map[int]subscriber
+	messages int
+	last        time.Time
+	ctx context.Context
+	cancel context.CancelFunc
+	mu sync.Mutex
+}
+
+type subscriber func(msg *message) error
+
+func newTopic(id string) *topic {
+	ctx, cancel := context.WithCancel(context.Background())
+	return &topic{
+		id:          id,
+		subscribers: make(map[int]subscriber),
+		last:        time.Now(),
+		ctx:         ctx,
+		cancel:      cancel,
+	}
+}
+
+func (t *topic) Subscribe(s subscriber) int {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+	subscriberID := rand.Int()
+	t.subscribers[subscriberID] = s
+	t.last = time.Now()
+	return subscriberID
+}
+
+func (t *topic) Unsubscribe(id int) {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+	delete(t.subscribers, id)
+}
+
+func (t *topic) Publish(m *message) error {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+	if len(t.subscribers) == 0 {
+		return errors.New("no subscribers")
+	}
+	t.last = time.Now()
+	t.messages++
+	for _, s := range t.subscribers {
+		if err := s(m); err != nil {
+			log.Printf("error publishing message to subscriber x")
+		}
+	}
+	return nil
+}
+
+func (t *topic) Close() {
+	t.cancel()
+}